Here is an online program that lets you receive your voice mails in your email and I believe it is in MP3 format.

I know you can do this with Vonage but it is in Wav format. Also with this you can have music or sounds in the background. I work on a plane so I have a plane buzzing in the background. They are supposed to be having celebrity voices soon, not sure when.

The only drawback is they have your pin number for the phone. You can have 3 messages saved and you can decide when you want each one played.